Photoluminescence imaging and spectroscopy is a contactless, nondestructive method of probing the electronic structure of materials, such as silicon semiconductor wafers, solar cells, as well as other workpieces and materials. In a typical photoluminescence process, light is directed onto a wafer or other workpiece (hereinafter collectively referred to as a “sample”), where at least some of the light is absorbed. The absorbed light imparts excess energy into the material via a process of “photo-excitation.” The excess energy is dissipated by the sample through a series of pathways; one such pathway is the emission of light, or photoluminescence. The intensity and spectral content of the photoluminescence is directly related to various material properties of the sample and, thus, can be used to determine certain characteristics of the sample, including defects, as discussed in U.S. Pat. No. 7,113,276B1, which is incorporated herein by reference.
Reflectance or reflectivity imaging is a contactless, nondestructive method of probing the surface with a broadband illumination source and analyzing the intensity and spectral content of the signal bounced back from the surface. The surfaces typically can be classified into specular or diffuse surfaces and real objects typically exhibit a mixture of both properties.
It is sometimes desirable, e.g., for semiconductor wafer inspection applications, to measure intensity and spectral content of the photoluminescence and reflectance of the semiconductor wafer-size workpiece for the purpose of quality inspection in the same apparatus either concurrently or in a short sequence, with single wafer load, while achieving a high measurement throughput combined with high measurement spatial and spectral resolution.
Conventionally, spectral photoluminescence or combined spectral photoluminescence and reflectance are measured using a single point-by-point inspection solution. In a point-by-point solution, the sample is placed on an X-Y motion (or R-Θ) system and is illuminated and measured at a single excitation point. The sample is moved to another measurement point and again illuminated and measured. By repeating the translation of the sample in the X-Y directions, a photoluminescence and reflectance maps could be constructed from the point-by-point measurements. This solution, however, is inherently slow and therefore impractical in the full wafer inspection systems, especially at large specimen sizes, close to and above 100 mm in diameter, due to the low throughput.